// position
.static {
  position: static;
}

.fixed {
  position: fixed;
}

.sticky {
  position: sticky;
}

.relative,
.rela {
  position: relative;
}

.absolute,
.abso {
  position: absolute;
}

// 居中定位
.t-center,
.transform-center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.f-center,
.flex-center {
  display: flex;
  justify-content: center;
  align-items: center;
}